whats the highest gearing I should use?

[Urgeoner]

Okay right now I'm using the stock 18t mamba monster pinion with a 65t spur on my Revo conversion. It's pretty slow
I was thinking that the gearing is too low and want to step up a little.
It is very hot in Nebraska and humid as well, and I don't want to overheat obviously, and I was thinking of maybe getting a 58t spur and a 22-24t pinion..any help would be great as to what would be an ideal setup.
Oh and I got two of these 2s batteries hooked in series are these good for bashing/racing?
http://aircraft-world.com/shopexd.asp?id=6229